Detoxification studies using noxious lipophilic foreign and endogenous compounds have continued with conjugation reactions by genetically regulated (at the Ah locus) and phenobarbital inducible UDP glucuronosyltransferase activities. Different transferase activities using 21 substrates have been characterized for charge heterogeneity using a chromatofocusing system. It was shown that transferase enzymes generally have either a high (approximately pI 8.5) and/or a low (approximately p 6.7) isoelectric point such that 19 of 21 substrate activities varied independently after inducers treatment. 3-Methylcholoanthrene induced primarily high pI form(s), while phenobarbital induced both high and low pI forms. Activities for the 12 benzo[a]pyrene phenols also segregated into these two categories. Antibodies against a purified low pI form recognize only this form and not a high pI form. These results suggest many different forms of transferase.